Octadecanoic acid, C16-20-branched alkyl esters

Endpoint summary

Description of key information

Skin sensitisation (target: QSAR; source: LLNA, GPMT, Buehler): not sensitising

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Analogue justification

There are no data on the skin sensitisation potential of octadecanoic acid, C16-20-branched alkyl esters (CAS 85203-92-5). The assessment was therefore based on QSAR modelling and studies conducted with analogue (source) substances as part of a read across approach, which is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. For each specific endpoint the source substance(s) structurally closest to the target substance is/are chosen for read-across, with due regard to the requirements of adequacy and reliability of the available data. Structural similarities and similarities in properties and/or activities of the source and target substance are the basis of read-across. A detailed justification for the analogue read-across approach is provided in the technical dossier (see IUCLID Section 13).

Skin sensitisation

QSAR predictions

CAS 85203-92-5

The potential for the C18/C16 component and C18/C20 component of octadecanoic acid, C16-20-branched alkyl esters to be skin sensitisers was predicted in the QSAR OECD Toolbox (WoE, 2016). The results for these components are considered to be representative of the target substance. There was no alert for skin sensitisation potential estimated based on protein binding potential, in the Danish EPA database (C18/C16- and C18/C20 component).

In vivo

CAS 3687-46-5

The skin sensitising potential of decyl oleate (CAS 3687-46-5) was evaluated in a local lymph node assay (LLNA) performed according to OECD 429 and under GLP conditions (WoE, 2010). 25 µl of a 25 and 50% suspension, and 100% (undiluted) test substance in acetone/olive oil (4:1 v/v) was applied to the dorsal surface of both ears of 5 CBA mice/dose for 3 consecutive days. On Day 6, each animal was injected via the tail vein with 0.25 mL sterile phosphate buffered saline containing 20 µCi of 3H-methyl thymidine. After approximately 5 hours, the mice were sacrificed and the draining lymph nodes of the ears were excised. The nodes were pooled for each animal in PBS and the DNA precipitated with 5% TCA at 4 °C overnight. Slight edema (score 1 of 4) was noted on the ears of 5/5 mice treated with the undiluted substance. This is not considered to have had a significant effect on the activity of the lymph nodes. All the nodes of the animals in the control and treatment groups were normal in size, and no macroscopic abnormalities were noted in the surrounding area. The reliability check performed with hexyl cinnamic aldehyde was valid as the positive control group. The mean DPM/animal values for the control, 25, 50 and 100% groups were 488, 571, 951 and 1013, respectively. The SI values calculated for the 25, 50 and 100% groups were 1.2, 2.0 and 2.1, respectively. An SI > 3 indicates a skin sensitising potential. As all SI values were < 3, the test substance is considered to be not skin sensitising. 

CAS 93803-87-3

A Guinea pig maximisation test was performed with 2-octyldodecyl isooctadecanoate (CAS 93803-87-3) under GLP conditions and using a protocol similar to OECD guideline 406 (WoE, 1991). 10 test and 5 control Himalayan guinea pigs were induced intradermally with undiluted test substance on both sides of the spine with and without Freud's complete adjuvant. On Day 7, the animals were treated with 10% sodium dodecyl sulfate to induce mild skin irritation. On Day 8, a 48-hour epicutaneous induction treatment with the undiluted test substance was performed under semi-occlusive conditions. On Day 22, the challenge treatment was performed by topical application of the test substance at 100% (right flank) and a blank patch (left flank) to all animals for 24 hours, under semi-occlusive conditions. Skin reactions were evaluated 24 and 48 hours after the challenge application. During the study, no test substance-related clinical signs and no effects on body weight gain were observed. 8 hours after intradermal induction, slight to severe erythema was noted at all of the sites injected with FCA/water and FCA/test substance in 10/10 treated and 5/5 control animals. 4/5 control animals also exhibited necrosis at the FCA/test substance injection site. In 3/10 treated animals slight to well-defined erythema was observed at the injection site of the test substance. Following the topical induction, severe erythema and scabs were observed at the test site in 3/10 treated animals. A further 4/10 (in total 7/10) treated and 4/5 control animals exhibited only scabs. No skin reactions were observed after the challenge treatment in any of the animals of the test and control groups. The results of the reliability check carried out at regular intervals were positive, confirming the reliability of the assay. Based on the results, the test substance showed no skin sensitising effect in guinea pigs.

CAS 17673-56-2

The skin sensitising potential of (Z)-octadec-9-enyl (Z)-docos-13-enoate (CAS 17673-56-2) was evaluated in a Buehler test performed according to a protocol similar to OECD 406 and under GLP conditions (WoE, 1995). The induction treatments were performed on 20 Dunkin Hartley guinea pigs on Day 0, 7 and 14. A 70% solution of the test substance in peanut oil was applied to the shaved skin on the flank of the animals, and covered with an occlusive dressing for 6 hours. On Day 28, all the animals were challenged with a 60% solution of the test substance via topical application on the flank for 6 hours, using an occlusive dressing. 10 guinea pigs in the control group were treated according to the same protocol with the vehicle as the control substance. During the first reading, 1/20 treated animals and 1/10 negative control animals had a positive reaction, respectively. In the second reading, 2/20 treated animals and 1/10 negative control animals had a positive reaction, respectively. The slight, patchy erythema was limited to the left flank, where both the induction and challenge doses were applied. It is possible that the reaction was skin irritation, rather than a sensitisation reaction. All skin irritation effects had cleared within 72 hours after the challenge exposure ended. The result of the reliability check was inconclusive. During the first challenge application with 25% alpha-hexyl cinnamic aldehyde, a sensitisation reaction was induced in 25% (5/20) of the Dunkin Hartley guinea pigs, while the second challenge application did not cause sensitisation reactions. In the negative control group, the first challenge application induced sensitisation in 20% (2/10) of the animals, and the second challenge application did not cause sensitisation reactions. The results of the study are still considered to be valid as the first results could not be reproduced. Under the conditions of this study, the test substance is considered to be not skin sensitising.

Conclusion

A weight-of-evidence approach was applied to assess the skin sensitising potential of the target substance octadecanoic acid, C16-20-branched alkyl esters. The 2 main components of the target substance were screened in the OECD QSAR Toolbox v3.3. No structural alerts for protein binding specifically related to skin sensitisation potential were identified in the Danish EPA database. Hence, none of the individual components are likely to cause skin sensitisation. In vivo studies (LLNA, GPMT, Buehler test) performed with 3 source substances all gave negative results. Overall, octadecanoic acid, C16-20-branched alkyl esters is not expected to be skin sensitising. 

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

Study not required according to Annex VII-X of Regulation (EC) No 1907/2006.

Justification for classification or non-classification

According to Article 13 of Regulation (EC) No. 1907/2006 "General Requirements for Generation of Information on Intrinsic Properties of substances", information on intrinsic properties of substances may be generated by means other than tests e.g. from information from structurally related substances (grouping or read-across), provided that conditions set out in Annex XI are met. Annex XI, "General rules for adaptation of this standard testing regime set out in Annexes VII to X” states that “substances whose physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be considered as a group, or ‘category’ of substances. This avoids the need to test every substance for every endpoint". Since the analogue concept is applied to octadecanoic acid, C16-20-branched alkyl esters (CAS 85203-92-5), data will be generated from data for reference source substance(s) to avoid unnecessary animal testing. Additionally, once the analogue read-across concept is applied, substances will be classified and labelled on this basis.

Therefore, based on the analogue read-across approach, the available data on skin sensitisation do not meet the classification criteria according to Regulation (EC) 1272/2008 and are therefore conclusive but not sufficient for classification.